The present invention relates to a flame detector that performs detection of flames by capturing light having a wavelength unique to flames.
A related-art flame detector has a main detection light-receiving element that receives infrared radiation from a front aperture of a housing, to thus detect flames; a light-receiving window made up of a transmission plate that is positioned in front of the main detection light-receiving element and that permits transmission of infrared radiation; a test light source that illuminates test light for detecting stains on the light-receiving window; a test light-receiving element that receives the test light passed through the light-receiving window, to thus determine the degree of the stains on the light-receiving window; and an operation indicator lamp that becomes illuminated at the front side of a housing (see; for instance, JP-A-2005-122437).
A requirement for the flame detector is that the operation indicator lamp should be readily and clearly visible from all directions with reference to a center line (a direction perpendicular to the front) of the detector. Accordingly, the related-art flame detector has a floodlight window forwardly projecting from a vertex portion of a front head of a housing, and the window receives inside light from the light emitting element serving as a main light source and provides a luminous indication to the outside.
Due to this structure, in the related-art flame detector, the operation indicator lamp is positioned on one side with reference to the center of the front of the housing. Therefore, the related-art flame detector has a problem that the visibility from the other side is not good.
Further, in order to even slightly improve omnidirectional visibility, the operation indicator lamp must be projected from the front of the housing. Accordingly, the indicator lamp becomes thick in its front-to-back direction, which in turn raises a problem of an increase in the overall size of the detector in its front-to-back direction.
In order to receive light of predetermined wavelength from the outside, the light receiving part of the main detection light receiving element for flame detection used in the flame detector must be arranged so as to oppose the front and be able to receive light. In order to enable stable detection of flames at all times, deterioration of detection accuracy, which would otherwise be caused by satins on a translucent plate that is to serve as a cover for the main detection light receiving element, must be monitored. In this regard, in the related-art flame detector, a concave portion is provided in the front of the housing, the test light source is disposed inside an inner wall of the concave portion, test light is emitted from the test light source on a test light receiving element disposed inside the floodlight window, and stains on the translucent place are monitored by the quantity of light received.
However, in the above stain detection structure, the test light must be emitted from a position ahead of the translucent window. The test light source must be positioned distant from a circuit board placed in the vicinity of an interior rear side of the housing. Further, a connection with the circuit board by way of a socket and supporting of legs of the element by a member that supports the legs in an extended manner are required. An increase in the number of components and deterioration of productivity of the flame detector are therefore brought about.